Browsing by Author "Medhn, Samuel"

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    Cooperative MIMO System for WiMAX Technology
    (Addis Ababa University, 2012-09) Medhn, Samuel; Hailemariam, Dereje (PhD)
    Multipath fading is one of the primary factors that degrade the performance of wireless networks. One of the most powerful techniques to combat the effect of fading is by using multiple antennas that provides space diversity and spatial multiplexing; this technique is called Multiple-Input Multiple-Output (MIMO). Cooperative diversity, an alternative form of realizing MIMO, has been recently proposed to realize the diversity advantage in a distributed manner. Cooperative diversity exploits the broadcast nature of wireless transmission and creates a virtual antenna array through cooperating nodes. Although, prior research in cooperative diversity considers users equipped with single antenna, in practical scenarios users may be able to accommodate multiple antennas due to the recent advances in semiconductor industry. Hence, the primary purpose of this thesis is to model, and by using simulation, investigates the end-to-end performance of a cooperative diversity system employing multi-antenna at cooperating nodes; the intention is to simultaneously exploit the diversity gain offered by the cooperative diversity and multiple antennas. One contribution of this work is, we propose a cooperative MIMO system where the cooperation uses amplify-and-forward (AF) relaying strategy and the MIMO is based on Vertical Bell-Labs Layered Space Time architecture (VBLAST). The proposed system is to be used for WiMAX technology. Complexity of the cooperative MIMO system is also analyzed considering Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) schemes for Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Maximum Likelihood (ML) detection techniques. Simulation results show that cooperative MIMO system achieves significantly better symbol error rate (SER) performance than conventional cooperative diversity and MIMO systems with comparable complexity. As an example, for SER of 10-3, cooperative MIMO system using MMSE detection has 10 dB SNR gain over systems that employ cooperative diversity or MIMO only. Key words: Cooperative Diversity, MIMO, AF, VBLAST, WiMAX, SER, Complexity